Method of conditioning brightening baths



Patented Jan. 13, 1953 BAT Stanleylt. Prance and Harold J. Reindl, Dayton,

Ohio, assignors to General Motors Corporation, Detroit, Mich., a corporation of Delaware No Drawing. Application May 3, 1951,

Serial No. 224,459

Claims.

This invention relates to a method for the control and conditioning of a chemical brightening bath for aluminum and/or its alloys.

It is, therefore, the main object of this invention to provide a method of control whereby a chemical brightening bath for aluminum and/ or its alloys may be conditioned whereby the effectiveness of the bath is maintained at a uniform level.

A further object of the invention is to provide a method for conditioning and controlling chemical brightening baths for aluminum and/or its alloys wherein the bath consists essentially of nitric acid together with ammonium and fluoride ions and a carbohydrate, said bath preferably including small quantities of chromic acid and a soluble metal salt. Specifically, one of such baths is disclosed in our copending application, Serial No. 191,324, now Patent No. 2,614,913, although the constituents, making up the bath, may vary providing the bath includes the ions of nitrates, fluorides, ammonium, chromates, to gether with one of the glycols.

Another object of the invention is to provide a method for conditioning brightening baths of the character described, wherein additions to the bath are made in predetermined quantities for each square foot of aluminum and/or aluminum alloy treated in each gallon of the bath. Specifically, the invention comprehends the removal and replacement of from .004 to .01 of a gallon for each gallon of bath for each square foot of aluminum or aluminum alloys treated therein.

Another object of the invention is to provide a conditioning method for chemical brightening baths for aluminum and/or aluminum alloys wherein the additionsto the bath used for control are over and above the regular addition necessary for use during the'brightening process.

Further objects and advantages of the present invention will be apparent from the following description.

Numerous types of chemical brightening baths have been used in connection with aluminum and/or its alloys. Baths having a high viscosity, such as, baths including phosphoric acid in large quantities, have high drag-out losses, and therefore are expensive to maintain. Baths including nitrates, fluorides and chromates, such as, for

example, the bath described and claimed in application, Serial No. 191,324, new Patent No. 2,- 614,913, are of low viscosity and include a major portion of water and are therefore inexpensive to utilize and due to the fluidity of the bath have a low drag-out loss.

On the other hand, these later baths do not have as long a useful period of life as is present in the phosphoric acid baths, necessitating a periodic disposal of the entire-bath together with the use of an enti l n whath olution;

. '2 In our cope'nding application, Serial No. 191,- 324, a specific bath is set forth having a formula as follows:

This bath may be modified by using cane sugar dissolved in the bath in place of ethylene glycol within the range of .20% to .0% with a 30% preferred and similarly ammonium fluoride may be used in place of ammonium bifluoride within the same ranges. The bath is made up with water as a base and is operated at an elevated temperature, for example, in the order of 185 F. to 212 F.

We have found that this type of bath generally reaches a point of little value after treatment of from to 250 square feet of aluminum and/or aluminum alloy per gallon of bath depending on the degree of brightnessdesired. We have further found that the baths effectiveness reduces progressively with the square footage of aluminum and/or aluminum alloy treated up to a point where the bath is generally completely unuseable when '250 square feet of aluminum has been treated in a gallon of the bath.

In view of this fact we have done considerable work in an efi'ort to improve, the useful life' of the bath and thereby reduce the cost of using the bath while simultaneously obtaining an improved producttherefrom for, in most cases, after square feetof aluminum has been treated .in a gallon of bath,' -the brightness of the aluminum has been so reduced as to make the bath .of doubtful use commercially;

3 We therefore have discovered that if a predetermined quantity of the bath is removed periodically and replaced with a like quantity of fresh bath, the efiiciency and life of the bath may be maintained throughout an indefinite period of time. This removal and addition may take the form of a continuous removal and continuous additionror may take the formof a periodic removal and periodic addition of freshabathj. In other words, so long as the quantities noted hereinafter are removed and replaced for-a given area of aluminum treated, the exact method. for addition and removal of the bathis of small consequence. 1 V

, Specifically, we have found that for 'each square foot of aluminum treatedin' a gallon of the bath that between .004 and 101* ofyagallon of .the bath should be removed and replaced with fresh bath. bismeans that after 100 to 250 square feet of aluminum is treated per. gallon of bath, the entire bath has been effectively re placed. It is apparent that during this removal and addition on a periodic or continuous basis, all of the old bath has not been completely removed but rather has been continuously boosted in efiiciency to a satisfactory commercial level. It should be noted that the materials to be added. as hereinbefore described, are in addition to the usual periodic additions as suggested in our copending application, Serial No. 191,324.

These periodic additions are made in the fol-- lowing manner as determined by the brightness of the parts being treated and/or by analysis of bath concentrations for each square foot of surface brightened we add in the order of 8.5 cc. nitric acid, .75 gram of ammonium bifluoride and .75 cc. of ethylene glycol or .4 gram of sugar. Water may be added simultaneously to maintain the lever of the bath to a given point within the brightenin tank.

We prefer to utilize a brighteningv bath wherein ammonium bifluoride is a salt used to include both the ammonium and fluoride ion although it is understood that ammonium fluoride or hydroiiuoric acid and ammonia may all be used. Similarly, glycerine, ethylene glycol, sugar, alcohol or other carbohydrates, etc., may be used as brighteners whereas metal salts, chromic acid, nitric acid and water make up the remainder of the bath.

For bright treated objects the upper end of the range should be used, namelly, .01 of a gallon addition for each square foot, whereas, for commercially bright objects wherein a high degree of brightness is not required, the lower end of the range or .004 gallon addition for each square foot of aluminum may be used, these factors being a matter of choice. All such variations come fully within the scope of our invention, which comprehends the control and conditioning of a bath having as its essential ingredients, fiuorides, nitric acid, ammonium ions, chromic acid and soluble salts of metals such as copper, etc., together with a polyhydric alcohol.

While the embodiments of the present invention as herein disclosed, constitute preferred forms, it is to be understood that other forms might be adopted.

What is claimed is as follows.

1. In the method for brightening aluminum and aluminum alloy parts in a chemical bath and simultaneously maintaining the effectiveness of the bath wherein the bath consists essentially of an aqueous solution of nitric acid together with the ions of ammonium and fiuo ride, a metal and chromic acid and a carbohydrate, the steps comprising; dipping aluminum and/or aluminum alloy parts into said bath for brightening the surface of said parts, removing between .004 and .01 of a gallon per gallon of said brightening bath for each square foot of aluminum and/or aluminum alloy treated there in, and adding new solution of the same composition as the initial bath in equal quantity to the removal, whereby the brightening action of the bath is maintained substantially constant.

2. In the method for brightening aluminum and aluminum alloy parts in a chemical bath and simultaneously maintaining the effectiveness of the bath wherein the bath consists essentially of an aqueous solution of nitric acid .together with the ions of ammonium and fluoride, a metal and chromic acid and a carbohydrate, the steps comprising; dipping aluminum and/or aluminum alloy parts into said bath for brightening the surface of said parts. removing increments of the brightening bath not in excess of .01 of a gallon per gallon of the bath for each square foot of aluminum and/or aluminum alloy treated therein and adding increments of equal quantity of the same composition as the initial bath to the bath whereby the volume and brightening action of the bath is maintained constant.

3. In the method for brightening aluminum and. aluminum alloy parts in a chemical bath and simultaneously maintaining the effectiveness of the bath wherein the bath consists essentially of an aqueous solution of nitric acid together with the ions of ammonium and iiuoride, a metal and chromic acid and a carbohydrate, the steps comprising; continuously clipping aluminum and/or aluminum alloy parts into said bath for brightening the surfaces of said parts and continuously removing said parts from the bath after their surfaces have become brightened, continuously removing portions of the bath so as not to exceed .01 of a gallon per gallon for each square foot of aluminum and/or aluminum alloy treated therein, and constantly adding new bath of the same composition as the initial bath in quantitiesequal to the removed quantity, Whereby the volume and brightening action of the bath is maintained substantially constant.

4. In the method for brightening aluminum and aluminum alloy parts in a chemical bath and simultaneously maintaining the effectiveness of the bath wherein the bath consists essentially of an aqueous solution of nitric acid to ether with the ions of ammonium and fluoride, a metal and chromic acid and a carbohydrate; the steps comprising; dipping aluminum and/or aluminum alloy parts into said bath for brightening the surfaces of said parts, removing portions of the bath when the efficiency thereof commences to decrease and adding like quantities of fresh bath of the same composition as the initial bath for maintaining the brightening efliciency of the bath at a substantially constant level.

5. In the method for brightening aluminum and aluminum alloy parts in a chemical bath and simultaneously maintaining the effectiveness of the bath wherein the bath consists essentially of an aqueous solution including the ions of nitrate, fluoride and ammonium together with a brightener, the steps comprising; continuously dipping aluminum and/or aluminum alloy parts into said bath for brightening the surfaces of said parts and continuously removing parts from said bath after their surfaces have become brightened, continuously removing portions of the bath so as not to exceed .01 of a gallon per gallon for each square foot of aluminum and/or aluminum alloy treated therein, and constantly adding new bath of the same composition as the initial bath in quantities equal to the removed quantity, whereby the volume and brightening action of the bath is maintained substantially constant.

' STANLEY R. FRANCE. HAROLD J. REINDL.

REFERENCES CITED UNITED STATES PATENTS Name Date- Waldpian et al. June 12, 1945 Number 

1. IN THE METHOD FOR BRIGHTENING ALUMINUM AND ALUMINUM ALLOY PARTS IN A CHEMICAL BATH AND SIMULTANEOUSLY MAINTAINING THE EFFECTIVENESS OF THE BATH WHEREIN THE BATH CONSISTS ESSENTIALLY OF AN AQUEOUS SOLUTION OF NITRIC ACID TOGETHER WITH THE IONS OF AMMONIUM AND FLUORIDE, A METAL AND CHROMIC ACID AND A CARBOHYDRATE, THE STEPS COMPRISING; DIPPING ALUMINUM AND/OR ALUMINUM ALLOY PARTS INTO SAID BATH FOR BRIGHTENING THE SURFACE OF SAID PARTS, REMOVING BETWEEN .004 AND .01 OF A GALLON PER GALLON OF SAID BRIGHTENING BATH FOR EACH SQUARE FOOT OF ALUMINUM AND/OR ALUMINUM ALLOY TREATED THEREIN, AND ADDING NEW SOLUTION OF THE SAME COMPOSITION AS THE INITIAL BATH IN EQUAL QUANTITY TO THE REMOVAL, WHEREBY THE BRIGHTENING ACTION OF THE BATH IS MAINTAINED SUBSTANTIALLY CONSTANT. 